Transmission lines are exposed to faults due to bad weather (hurricanes, lightning), insulation breakdown, short circuits by birds, and contact by tree branches and other objects. Temporary faults are cleared by tripping then autoreclosing. For permanent faults, the power supply is restored only after the maintenance crew finds and replaces the failed component. For this purpose, precise fault location should be known, else the fault location identification job turns out to be tedious and time consuming for long transmission lines spread across rugged terrains such as hilly areas, mountains, and deserts, etc. Visual inspection techniques are advanced, from road patrols to air patrols and, more recently, to trials with drones and unmanned aerial vehicles, etc. These methods may not be cost effective for long transmission lines. Identification of fault location with high precision on transmission lines is of great value to transmission asset owners and maintenance crews as it helps in expediting maintenance work and achieving quick restoration of the line. Quick restoration of service improves the reliability of power supply and reduces the financial loss for the utilities and end users.
Traveling wave (TW)-based fault locators are used to locate the fault within a 1-2 tower span distance. The performance of TW-based fault location methods depends on accurate detection of wavefront arrival times, sampling rate, and data synchronization. The single-ended TW-based methods use the incident and reflected wave arrival times to locate the fault. The single-ended TW-based techniques pose challenges in identifying the waves reflected from the location of the fault and the remote substation terminals, as well as the waves reflected from the buses of adjacent networks connected to the protected line. Therefore, the practical implementation of the single-ended TW-methods is challenging and limited. Two-ended TW-based methods are more accurate, and these methods are in practical use. However, accuracy of TW-based fault location algorithms depends on traveling wave detection, data synchronization, IED hardware, processing of multiple reflections, filtering of noise, correction of substation secondary cable delays, and wave speed, etc. These data synchronization and wave speed errors can be corrected by conducting experiments such as creating a fault at a known distance and calculating the secondary cable delays and wave speed. This process is difficult, requires more engineering effort and is not cost-effective. Besides, they are not economical solutions for transmission asset owners due to the high cost involved in dedicated hardware and solution tuning efforts.
Present communication technology allows for the use of data from all ends of the line to calculate the location of the fault. This offers an economical alternative to TW-based methods that require high IED sampling rates. For the fault location methods presented in this paper, one IED is required at each end of the line, and each IED must be connected to each other IED via a 2Mbps communication link. At each line-end, the local currents and voltages are connected to the local IED, which digitizes these inputs to obtain sampled values of the local currents and voltages. Each local IED sends these sampled values to the remote IED/s. Hence all remote IEDs receive the currents and voltages from the local IED as sampled values. The IEDs need to be time coordinated (time synchronized) so that, on receipt of the current and voltage sampled values from a remote IED, the local receiving IED can time coordinate these with its current and voltage sampled values, and interpolate as required to obtain remote values that are time aligned with the local values. Each IED therefore has available to it time aligned sampled values of the local and all remote currents and voltages. It is from these sampled values that the pre- and during-fault positive-sequence phasors are calculated.